Synthesis of zeolites A and X from fly ashes and their ion-exchange behavior with cobalt ions

Abstract

A modified fusion process was studied to synthesize zeolites A and X from fly ash. It was found that the addition of aluminum hydroxide to the fused fly ash solution followed by hydrothermal treatment at 60°C produced single-phase zeolite A or a mixture of zeolites A and X depending on the source of the as-received fly ash. The result confirms that the quantity of dissolved Al species is critical for the type of zeolite formed in precursor solutions prepared from fused fly ashes. The ion-exchange behaviors of treated fly ashes containing zeolites A and X were tested with Co2+ ions. It was found that the ion-exchange capability (IEC) of treated fly ash with Co2+ ions was much larger than that with Cs+ ions. In addition, the Co2+ ion-exchange rate of zeolite X was faster than that of zeolite A. This is probably related to the bigger pore channels in zeolite X. The Co2+ IEC of treated fly ash containing zeolite A reached 67.6% of commercial zeolite A and that containing zeolite X 83.1% of commercial zeolite X. Our study demonstrated that fly ashes can be converted to zeolites A and X, and these treated fly ashes have great potential for removing heavy metals.